You will need a friction front shifter, but I assume you are using the stock friction bar end shifter so that should not be a problem for you. I think you should consider a 24t instead of a 26t if you want climbing ability.
I have a 52/42/24 front (Campy) and an eight speed 11-32 (11/12/14/16/18/21/26/32 SRAM) rear. I replaced the 30t smallest chainring with a generic aftermarket 24t. I have enough chain so that if I shift onto the largest front chainring (52t) and rear sprocket (32t), that I don't jam anything up. Unfortunately that is a couple more links than most chains are sold with on my LHT. With this gearing there is too much chain if I use the 24t front and the smallest (11t or 12t) sprockets on the rear, the rear cage won't wrap up all of the chain. But, I avoid using the two most cross chained gears with each chainring, so that means that I actually only use 18 of my 24 gears. Thus, this works great for me.
I can't comment on your front and rear derailleurs, I have a M739 XT rear and a vintage Suntour front, both work well for me. Shifting from the 24t up to the 42t chainring is not a smooth shift but I can usually make that shift in a distance of 25 to 50 feet. I set up my LHT with this gearing when I built it in 2004 and I liked this gearing so much that when I built up another touring bike a year ago, I set that bike up with identical components.
You should consider a chain catcher to make sure that the chain lands on the 24t (or 26t) on the downshift. I have not had any problems before I installed a catcher but a friend often had his chain fall onto the bottom bracket shell when he downshifted. I installed one as an insurance policy.
